This application relates to control systems, and more particularly to cross-coupled multivariable control systems.
In control theory, a given control system may have a plurality of goals and a plurality of limits. Limits are inequality constraints on system dynamic variables. An example limit may be to prevent an engine temperature from exceeding a certain temperature in order to prevent meltdown or rapid deterioration. Another might be to prevent a rotor speed from exceeding a certain angular velocity to maintain structural integrity. An example goal may be to achieve a certain engine thrust level, such as a thrust of 10,000 pounds. While it is desirable to achieve goals, it is necessary to meet limits. A multivariable system may include a number of effectors that can be adjusted to meet system goals and limits. In some cases, a system may be cross-coupled, which means that each effector change may affect goals and limits with varying dynamics. In a cross-coupled system, it is not possible to change a single effector in isolation to affect only single goal or limit, as a change in one effector may affect a plurality of goals or limits. Calculating effector commands in a cross-coupled multi-variable system can therefore be complex and computationally demanding, and it may be necessary to prioritize goals in order to meet all limits while best meeting a number of goals.
Most existing control systems are directed to single input, single output systems, or a system with a collection of inputs and outputs that are only loosely coupled. Cross-coupled multi-variable systems cannot be adequately controlled with such models. While some existing model predictive control technology can address both cross-coupled multi-variable requirements while enforcing limits, application of such technology has been limited to chemical process applications, which require updates only once every several minutes. Such a computational burden is not practical in a system, such as a vehicle control system, where updates may be required on the order of one hundred times per second.